Various systems for determining the efficacy of sterilization processes are known in the art. There are several types of indicators used in the field, each providing various levels of assurance to the user that the appropriate processing requirements were met.
One of the most important classes of indicators are the biological indicators (BI). BIs provide the highest degree of assurance that sterilization conditions were met within the processor or processed load itself. This type of indicator is designed to represent the worst case for the processing system by providing an extremely high number of highly resistant organisms to that particular process within or on the indicator. Usually spores are the organism of choice for monitoring sterilization systems.
Biological indicators include microorganisms inoculated onto a carrier material. The microorganisms are typically bacterial spores which are known to be very resistant to the particular sterilization medium in which they are to be used. The carrier is placed into a sterilization cycle along with the medical device load. Following completion of the cycle the bacterial spores within the biological indicator are incubated and monitored for growth over periods of up to seven days. Growth of the bacterial spores in the biological indicator indicates that the sterilization process was not efficacious. No growth of the biological indicator confirms that conditions within the sterilizer were adequate to kill at least the number of bacterial spores loaded onto the indicator (e.g., 106 bacterial spores) and therefore provides a level of assurance that the medical device load is sterile.
Due to many factors, there is a need in the hospital setting for determination of the efficacy of the sterilization in the shortest possible timeframe. Prior art systems required 12-48 hours for this determination. More recently, fluorescence has been used to detect the activity of enzymes that are produced by the test organisms by adding a fluorogenic enzymatic substrate to the growth media. This methodology lessens the incubation time from days to hours. However, the main limitation for reducing the incubation time beyond that seen for this methodology is the requirement for the pre-incubation and subsequent fluorescence monitoring of the biological indicator. These indicators have been designed primarily for the purpose of containing the biological indicator cells in a manner and form consistent with the requirements for placement in the sterilizer under evaluation and not necessarily for ease of use in the subsequent fluorescence detection steps.
One such product that permits early evaluation of a biological indicator exists that combines incubation with the simultaneous monitoring of fluorescent emissions, and requires determination of a baseline level of the emissions. This product minimally includes a single heater block that is set to one selected temperature, and a number of vertical holes into each of which one biological indicator may be placed. The heater block has horizontal through-holes which align with transmission panels in a biological sample container in the sample location, so that UV light from UV-emitting lamps may be passed through the biological sample. On a separate, moveable printed circuit board there resides a single detector that must be moved to align with each of the through-holes so that the detector passes in front of each sample location in turn. The movement of the detector is under the control of an on-board processor and requires moving parts. The detector is moved from one such sample site with through-hole to the next in a sequence and readings are taken for each sample present. An algorithm programmed into the controller logic is used to first determine a baseline level of fluorescence and then to detect the presence of fluorescence at a level above the baseline level. Based on the baseline and the reading obtained, an interpretation is made of a PASS (Negative) or FAIL (Positive) nature to advise the user if conditions were met in the sterilizer cycle being evaluated by the biological indicator.
In the prior art cited above, the reliance on moving parts introduces the potential for mechanical failures and/or light path misalignments. The movement of parts can generate or be interfered with by kinetic forces (vibration and mechanical shock) and can create wear on surfaces requiring periodic maintenance and/or recalibration. The presence of a single heat block means that only one temperature can be used by each machine at a given time or may require the purchase of a separate machine for use at different temperatures.
What is needed is a design that eliminates moving parts, wear points and other mechanical aspects that can impact the durability and performance of such a reader incubator, that eliminates variations in alignment of the light source, the biological indicator and the detector, that does not require the determination of a baseline or minimum level of fluorescence prior to initiating reading of test results, while at the same time provides an early and reliable indication of the efficacy of the sterilization process.